Okay first, the costume is fabulous. I actually have nothing negative to say about it. The colors are lovely. The wig looks wonderful (Not an accurate length but I think this looks better in real life mostly because it's not only a pain to try to keep 70 ft of hair untangled but nearly impossible and completely impractical) It's a lovely color though slightly flat looking. Not something I would bother doing anything to as you get the over all effect across.
Your makeup is fantastic. You look young and fresh. Your eyes look huge but not inhumanly so which is more important for this costume than one would think. None of your features are washed out.
I have only a couple things I would change. First, I think you should have stood to your right a couple more feet and turned to your left just slightly. We would still have gotten the effect of you looking at Maximus but would have seen your face better. The styling of the wig actually blocks a very pretty face.
Second, I think the post could use a bit more attitude. Raise your right arm slightly and put your left hand on your hip. That would let your left hand look like it has a purpose. Widen your stance to reinforce that adorable stern look of hers in this scene.
Love that picture. Really great and cute idea. And that horse! It looks exactly like Maximus And you make a good Rapunzel, too. Dress, wig and face expression are perfect. That you made the photoshoot despite your allergy is very admirable